Digital data is extremely convenient and well-adapted to distribution and copying without loss of quality. These valuable features, however, are also a threat to those who own the digital data. In some businesses it is necessary to maintain strict control over the reproduction and playback of valuable data. For example, databases, imagery, music, and personal information are all highly valuable digital commodities to which the owners might wish to restrict access.
The distribution of digital media has long been subject to security concerns and the piracy of digital content is a significant problem. Software, audio, and video content are routinely stolen and illegally re-sold. While the information on these disks can be encrypted, the customized encryption and decryption of the data is generally impractical for economic reasons and the distribution of decryption keys to a mass market is generally impractical for logistical reasons.
Many encryption techniques are known in the art which address these issues to a limited extent. For example, encryption techniques for rendering digital information unreadable without first decrypting the information with the use of keys is well-known. Generally, techniques use either the same key to encrypt and decrypt or use one key to encrypt and a second to decrypt. It is possible to do this without the encrypter or decrypter knowing what the key of the other is. Regardless of the encryption technique, maintaining the security of the keys themselves is problematic as is their distribution.
It is useful to distribute digital data, such as audio, video, or digital films to a large number of recipients while maintaining strict control over the contents and access to the contents. Doing so reduces the economic losses to the owners of the data content. The difficulties in doing this can be categorized as media control, copy control, and playback control. Obviously, these issues are interrelated.
For example, U.S. Pat. No. 5,745,568, issued Apr. 28, 1998 to O'Connor et al., entitled “Method of Securing CD-ROM Data for Retrieval by One Machine,” discloses a method for securing CD-ROM data for retrieval by a specified computer system. The data is encrypted with a hardware identifier as an encryption key. This identifier is associated with playback hardware and is used by the hardware to decrypt the data for playback.
This technique has several drawbacks for data having a large distribution. If a common encryption key for all instances of the data is used, access cannot be restricted to a sub-set of the hardware. If unique encryption for each data instance is used, a separate encryption step must be carried out on the data for each hardware playback device (or group of hardware devices with a common identifier). This encryption is tedious and costly; moreover, the management of the hardware identifiers at the data encryption site (i.e. key management) is problematic and a security risk. Secondly, this technique does not prevent unauthorized copying or playback of the information. Hence, an unscrupulous owner of two playback devices with a common identifier might copy the data and play it back in both machines while only having paid for the data once.
Moreover, once compromised, the hardware key is open to future exploitation with future data storage devices. Only by physically changing the hardware identifier can security be re-established.
Ha et al. in U.S. Ser. No. 09/393,527, filed Sep. 10, 1999, describe a method for controlling the copying of data sets on a mass-produced medium (Programmable Read-Only Memory for Compact Discs, or CD-PROM) by the use of software and disc identifiers adapted to authenticate a transferred program in the computer to permit the program to be operated by the computer. This technique does not prevent copying, per se, but rather inhibits the subsequent installation of copied software on computers through the use of disk identifiers which cannot normally be copied from disk to disk.
Again, the use of this invention for an application requiring a wide distribution and strict control over copying, access, and playback has some difficulties. For very high value data, the provision of the software identifier presents a security risk. If the media and the data identifiers are obtained illegally, there is no further protection for the data. Although a copy may not be installed on a computer (as described in the patent) it may well be played back an unlimited number of times in an unauthorized venue. In some applications, this may not be a problem, but in others (for example if the data is provided for public access or viewing) this is a serious problem. Although specially created machines adapted to copying, bit by bit, one CD-PROM to another might circumvent the disk identifier by copying it from one disk to another, the result will be of poor quality and available industry tools will not support it.
Moreover, this technique provides no control over the playback equipment. It may be desirable to limit access to the data to a particular set of playback machines to further enhance security. Finally, the technique makes no provision for encryption of the data and its subsequent decryption in a convenient way. Thus, someone who illegally obtains a data identifier and creates or modifies their own playback equipment may have unlimited access to the data and its playback.
There are many techniques known in the art for securely distributing computer software through insecure channels. Generally, these require encryption of the source data and using some variant of a public/private key technique for decryption and use. For example, U.S. Pat. No. 5,956,408, issued Sep. 21, 1999, to Arnold, entitled “Apparatus and Method for Secure Distribution of Data” describes privately encrypting software, distributing it, and then using the corresponding public key to decrypt it in a secure area within the destination computer.
Likewise, techniques for associating data with specific devices or addresses are known, for example, European Patent No. EP 0179612B11, granted Aug. 7, 1991 to Horn, entitled “Cryptographic System for Direct Broadcast Satellite Network.” Such systems typically require local knowledge of the identifier which is encrypted to provide a receiver key in some fashion. These methods do not provide verification of source media or data (although content accuracy can be digitally verified using known validation techniques) or partition keys as described herein. Note that this patent does not describe or claim data validation techniques. Such techniques can be used in addition to those described herein to provide yet another level of security and guarantee of data integrity.